On the second night of Pesach we begin the Mitzva of Sefirat Ha'omer, which requires that we count each night for seven weeks, until the festival of Shavuot. If one misses a night, he should count the Omer without a Beracha the following morning, and then may continue to count on the next night with a Beracha. If somebody forgot to count both during the night and the following day, then he should continue counting the following night, but without a Beracha.
The question arises whether one should count Sefirat Ha'omer with a Beracha if he already knows from the outset that he will be unable to complete the counting. Consider, for example, the case of a patient who is scheduled for an operation, Heaven forbid, at some point during the Omer period, and he knows that he will be anesthetized and will have to miss an entire day's counting. In such a case, should he count with a Beracha until he is forced to miss a day, or should from the outset count without a Beracha?
This question arises due to a ruling of the Mishna Berura concerning the Sefirat Ha'omer counting of women. Although women are exempt from the obligation of Sefirat Ha'omer, Ashkenazic women have the practice to recite Berachot when they perform Mitzvot from which they are exempt, and we would therefore expect that they should recite the Beracha before counting Sefirat Ha'omer. The Mishna Berura, however, writes that since women are likely to miss a day of counting, due to their busy schedules and many responsibilities, they should not recite a Beracha when they count, even if they do not miss a day. Seemingly, then, the same would apply to a man: if he knows from the outset that he will miss a day of counting, he should not recite a Beracha when counting Sefirat Ha'omer.
However, Rabbi Yosef Shalom Elyashiv (contemporary Halachic authority in Jerusalem) drew a distinction between men and women in this regard. The Mishna Berura's ruling applies only to women, since, as mentioned, they are not obligated in Sefirat Ha'omer in the first place. Men, however, are obligated by Halacha to count, and therefore even if a man knows at the beginning of the Omer period that he will have to miss a day of counting, he counts each night with a Beracha until that point.
Summary: One who misses an entire day of counting during Sefirat Ha'omer continues counting the following night, only without reciting a Beracha. If one knows from the outset that he will have to miss a day of counting, he nevertheless counts with a Beracha until he misses a day.
