Tayammum When Ghusl Is Not Possible After Operation
Question

I have had surgery and I have had my monthly period and I want to pray, what should I do? Should I do Tayammum? What is the way to do Tayammum following menses? Should I do Tayammum for each prayer?
Praise be to Allah.Tayammum when ghusl is not possible after operation
The woman who has her menses must do Ghusl (ritual bathing) when she becomes pure from menses and wants to pray. If she is unable to do Ghusl because she cannot get out of bed and thus unable to use water, or because the water will harm her, then she may do Tayammum. 
Shaykh Ibn Baz (may Allah have mercy on him) said: 
“Because Islamic Shari`ah is based on ease, Allah, may He be glorified and exalted, has made worship easier for those who are excused, according to their excuses, so that they will be able to worship Him without any hardship. Allah says (interpretation of the meaning):  
“and [Allah] has not laid upon you in religion any hardship.” [Al-Hajj 22:78] 
“Allah intends for you ease, and He does not want to make things difficult for you.” [Al-Baqarah 2:185] 
“So keep your duty to Allah and fear Him as much as you can.” [Al-Taghabun 64:16]
Also, the Prophet (peace and blessings of Allah be upon him) said: “When I command you to do a thing, do as much of it as you can” and said: “Indeed, the religion (of Islam) is easy.” 
If a sick person cannot (ritually) purify himself with water, by doing Wudu in the case of minor impurity or Ghusl in the case of major impurity, because he is unable to do so, or because he is afraid that it may make the sickness worse or delay his recovery, then he may do Tayammum , which means striking his hands once on clean dust , then wiping his face with the insides of his fingers and then rubbing his hands together, because Allah says (interpretation of the meaning): 
“And if you are ill, or on a journey, or one of you comes after answering the call of nature, or you have been in contact with women (by sexual relations) and you find no water, perform Tayammum with clean earth and rub therewith your faces and hands .” [Al-Nisa’ 4:43]
The one who is unable to use water comes under the same ruling as one who cannot find any water, because Allah says (interpretation of the meaning): 
“So keep your duty to Allah and fear Him as much as you can.” [Al-Taghabun 64:16]
And the Prophet (peace and blessings of Allah be upon him) said: “When I command you to do a thing, do as much of it as you can.” 
How should a sick person purify himself?
Shaykh Ibn Baz (may Allah have mercy on him) said:  
“Several scenarios may apply with regard to a sick person purifying himself : 
·        If his sickness is mild and there is no fear that using water may lead to death, severe sickness, delay of recovery or increase of pain, or if he is able to use warm water and that will not harm him, then it is not permissible for him to do Tayammum, because it is permitted in order to ward off harm, but he is not likely to be harmed. Also, since he can find water, then he is obliged to use it. 
·        If he has a sickness due to which he fears death or loss of a limb, or fears further sickness that may lead to death or limb loss, then it is permissible for him to do Tayammum, because Allah says (interpretation of the meaning): 
“And do not kill yourselves (nor kill one another). Surely, Allah is Most Merciful to you.” [Al-Nisa’ 4:29]
·        If he has a sickness which makes him unable to move and there is no one to bring him water, then it is permissible for him to do Tayammum. 
·        If he has wounds, sores, broken limbs or a sickness in which use of water will harm him, and he becomes Junub (major ritual impurity due to sperm discharge), it is permissible for him to do Tayammum, because of the evidence mentioned above. If he is able to wash the sound parts of his body then he must do that, and do Tayammum for the rest. 
·        If the sick person is in a place where there is no water and no dust, and there is no one who can bring him whichever of them if available, then he may pray as he is, and he should not delay the prayer, because Allah says (interpretation of the meaning):  
“So keep your duty to Allah and fear Him as much as you can.” [Al-Taghabun 64:16]” (Al-Fatawa Al-Muta`alliqah bil-Tibb wa Ahkam Al-Marda, p. 26) 
How to perform Tayammum after menses
The way in which to do Tayammum following menses is no different from the way of doing Tayammum in the case of minor impurity. 
Can you offer two or more prayers with one Tayammum?
Tayammum, like Wudu, removes (ritual) impurity, according to the correct view, so it is permissible to offer more than one obligatory prayer with it, and you do not have to repeat it for every prayer. 
So if you do Tayammum for Zuhr, for example, and you do not break your Wudu, it is permissible for you to pray `Asr with it, and so on. 
Shaykh Ibn `Uthaymin (may Allah have mercy on him) was asked: If a person does Tayammum for a Nafl prayer, can he offer an obligatory prayer with that Tayammum? 
He replied: 
“Tayammum removes impurity, so he can offer the obligatory prayer even if he did Tayammum for a Nafl prayer, just as if he did Wudu for a Nafl prayer, it is permissible for him to offer an obligatory prayer with the same Wudu. He does not have to repeat Tayammum if the time for the prayer ends, so long as nothing invalidated that Tayammum." (Fatawa Al-Shaykh Ibn `Uthaymin,  11/240)
And Allah knows best.